-Improved player queue stability by using more aggressive synchronization policy.

-Added sync buttons on live streams to allow seeking to live edge.
-Added custom cache key for extractor sources to allow more persistent reuse.
-Refactored player data source factories into own class and separating live and non-live data sources.

app/src/main/res/layout/activity_player_queue_control.xml

@@ -146,6 +146,16 @@
             android:textColor="?attr/colorAccent"
             tools:ignore="HardcodedText"
             tools:text="1:23:49"/>
+
+        <TextView
+            android:id="@+id/live_sync"
+            android:layout_width="wrap_content"
+            android:layout_height="match_parent"
+            android:gravity="center"
+            android:text="@string/live_sync"
+            android:textColor="?attr/colorAccent"
+            android:background="?attr/selectableItemBackground"
+            android:visibility="gone"/>
     </LinearLayout>
 
     <RelativeLayout